Unless you're really tall, go with S/M
It's really hard to know what size to go with for things like sleeves. I'm 6'0" and went with a S/M. Unless you're like 6'3" or have really long arms, don't go L/XL. I made that mistake (on a final sale) before I ended up ordering the S/M size.
The product itself is great! A little bit of warmth for the chilly fall runs, or some UV protection in the summer.